Advanced microwave phased array antenna systems will play an increasingly important role in communications and surveillance. The signal generation, control, transmission, distribution and signal processing at these high frequencies pose challenging problems, particularly when the number of antenna elements is large, the controller is remotely located from the antenna, the signal frequency extends to the millimeter wave range, or a larger signal bandwidth is required.
Phased array systems require fast, accurate control of the phases and amplitudes of multiple antenna elements for beam forming and steering. However, electronic techniques for controlling the phase of individual elements of the phased array require complex signal distribution and control networks to link up and control each individual antenna element using microwave electronic circuits at each antenna element which are relatively bandwidth limited.
FIG. 1 is a schematic diagram of a typical phased array antenna with prior art electronic beam steering circuits. Each antenna element 2 has associated with it an electronics module 3 which includes a microwave phase shifter 4. Since a typical phased array can have as many as 1000 antenna elements, this necessitates as many as 1000 individual phase shifters. The typical microwave phase shifter 4 at each antenna element 2 is based on a stepped microwave delay-line circuit. This circuit consists of several electronic switches and interconnecting microwave transmission lines. Several control signals (one for each bit) are required to set all the switches for each antenna element. This phase shifting scheme results in limited phase resolution, high loss, limited bandwidth and a complex controlling network. In a phased array antenna having on the order of 1000 antenna elements, each requiring several lines 5 to carry control signals, the complexity of the required controlling network will be apparent. In addition to this complexity, conventional transmission feeds using precision microwave guides and coaxial cables are increasingly less attractive due to large size, weight, and excessive transmission loss. Also, inadequate bandwidth capability and susceptibility to electromagnetic interference seriously limit the performance of such systems. And, only one beam from the array can be controlled at any one time.